Process for the production of photographic images

ABSTRACT

PROCESSED PHOTOGRAPHC SILVER IMAGES ARE STABILIZED BY THE ADDITION F ANTIBRONZING AGENTS AGAINST LOSS OF DENSITY AND CHANGES IN IMAGE TONE UPON HIGH GLOSS DRYING AT HIGH TEMPERATURES. COMPOUNDS WITH A HIGH ANTIBRONZING EFFECT ARE COMPOUNDS OF THE DIMERCAPTO-PYRAZOLO-PYRIMIDINE SERIES.

US. Cl. 96--52 5 Claims ABSTRACT OF THE DISCLOSURE Processed photographic silver images are stabilized by the addition of antibronzing agents against loss of density and changes in image tone upon high gloss drying at high temperatures. Compounds with a high antibronzing effect are compounds of the dimercapto-pyrazolo-pyrimidine series.

The invention relates to a process for the production of photographic images which includes drying mechanically at high temperatures on a high gloss press in effective contact with heterocyclic mercapto compounds as anti-bronzing agents.

The silver images obtained from light-sensitive silver halide emulsion layers often undergo changes during high gloss drying or during mechanical drying at high temperature. Thus commonly a loss in density occurs or blue-black image tones change to brownish tones and brown tones change into greenish black tones. These changes are known as partial burning or :bronzing of the silver image.

The incorporation of small quantities of certain chemical compounds, known as anti-bronzing agents, into the light-sensitive material which contains a silver halide emulsion copying layer is known. These compounds alternatively may be added to the treatment baths which are used for the material to prevent this loss of density.

The known anti-bronzing compounds are however, only of limited utility either because their anti-bronzing effect is not suflicient or because they impair the photographic properties.

It is among the objects of the present invention to provide new anti-bronzing agents which have a sufficiently large anti-bronzing effect and which do not deleteriously effect the photographic properties of the material.

We now have found that dimercapto-pyrazolo-pyrimidines of the following formula or the tautomeric thione compounds are excellent anti-bronzing agents:

Ezm w Y wherein R stands for alkyl containing l-12 carbon atoms, preferably 1-6 carbon atoms which may be substituted with phenyl, alkoxy having preferably up to 5 carbon atoms, hydroxy, sulfo or carboxyl, aryl, particularly a phenyl or naphthyl group, cycloalkyl such as cyclohexyl, triazinyl or pyrimidyl, these groups being substituted if desired, e.g. with alkyl or alkoxy groups both of which preferably contain up to 5 carbon atoms, aryl, hydroxyl, sulfo or carboxyl.

United States Patent 0 Numb er 3,695,880 Patented Oct. 3, 1972 Suitable compounds are shown in the following table:

Melting or decomposition point, degrees Examples of preparation of these compounds are as follows:

13.5 g. of 1-phenyl-4-cyano-S-aminopyrazole, 12.5 g. of potassium xanthate and 60 ml. of butanol are stirred together for 2 hours at to 1l0 C. The precipitate formed is removed by suction filtration in the cold and dissolved in water. 0n acidification with acetic acid, a colorless precipitate is formed which is recrystallized from methanol. 8.2 g. of 1-phenyl-4,6-dimercapto [3,4-d1- pyrazole-pyrimidine of melting point 270-273 C. are obtained. The other compounds in the above table are prepared in a similar manner.

The anti-bronzing agents are preferably added in dissolved form to the light-sensitive silver halide emulsion layer after chemical ripening or to the finished casting solution. Suitable solvents are Water, aqueous solutions of alkali metal hydroxides, lower aliphatic alcohols, for example those having up to 3 carbon atoms, dirnethylformamide or mixtures of these solvents.

T he anti'bronzing agents may also, of course, be added to other photographic layers or to the treatment baths, for example to the developer, the fixing bath, an additional hardening bath or to a bath which contains surface active compounds which is used as final bath before drying on the high gloss press or drying at elevated temperature.

The concentration of the anti-bronzing agent in the layers of the treatment baths may vary within wide limits. The concentration depends upon the effect required, the nature of the reproduction process or the composition of the photographic material. When used in a photo graphic layer, particularly in the silver halide emulsion layer, quantities of from 20 mg. to 1 g. per mol of silver halide have been found sufiicient. Concentration of between 200 and 700 mg. of anti-bronzing agent per mol of silver halide are preferred. When the anti-bronzing agents are used in treatment baths, they are preferably added in the form of their alkali metal salts. Also when they are used in this form their concentration is not critical. Optimum concentrations can easily be determined by a few simple laboratory tests. Concentrations of between 10 and 100 mg. per liter of treatment bath were found to be sufiicient. When added to the developer bath, quantities of only 20 to 50 mg. per liter are generally sufficient. The exposed photographic material passed through a bath which contains the anti-bronzing agent, absorbs a certain quantity of the compound in the water permeable layers. The anti-'bronzing agent diffuses into the layer which contains the silver image and is present during the drying at high temperature. The antibronzing effect obtained with this method is as good as that obtained when the compound is added directly to the silver halide emulsion laver.

The usual silver halide emulsions are suitable for use in the present invention. The silver halide may be silver acid and its derivatives such as salts, esters or amides, cellulose derivatives such as carboxymethylcellulose, alkyl celluloses such as hydroxyethylcellulose, starch or its derivatives such as ethers or esters or carragenates. Polyvinyl alcohol, partially saponified polyvinyl acetate, polyvinyl pyrrolidone and the like may be mentioned as suitable synthetic binders.

The emulsions may also be chemically sensitized for example by the addition of sulfur-containing compounds during chemical ripening, for example allyl isothiocyanate, allylthiourea, sodium thiosulfate and the like. Reducing agents for example the tin compounds described in Belgian Pat. No. 493,464 or 568,687 and polyamines such as diethylene triamine or aminomethylsulfinic acid derivatives, e.g. according to Belgian Pat. No. 547,323 may also be added as chemical sensitizers.

Noble metals or noble metal compounds such as gold, platinum, palladium, iridium, ruthenium or rhodium are also suitable as chemical sensitizers. This method of chemical sensitization is described in the article by R. Koslowsky, Z. Wiss. Phot. 46, 65-72 (1951).

The emulsions may also be sensitized with polyalkylene oxide derivatives, e.g. with polyethylene oxide having a molecular weight of between 1,000 and 20,000 or with condensation products of alkylene oxides and aliphatic alcohols, glycols, cyclic dehydration products of hexitols or with alkyl-substituted phenols, aliphatic diamines and amides. The condensation products have a molecular weight of at least 700 and preferably more than 1000. These sensitizers may, of course, also be applied in admixture with each other in order to achieve special effects, as described in Belgian Pat. No. 537,278 and in British Pat. No. 727,982.

The emulsions may also be optically sensitized, e.g. with the usual polymethine dyes such as neutrocyanines, basic or acid carboxyanines, rhodacyanines, hemicyanines, styryl dyes, oxonoles and the like. sensitizers of this type are described in The Cyanine Dyes and Related Compounds, F. M. Hamer (1964).

The emulsions may contain the usual stabilizers, e.g. homopolar or salt-type compounds of mercury with aromatic or heterocyclic rings such as mercaptotriazoles, simple mercury salts, sulfonium mercury double salts and other mercury compounds. Azaindenes, especially tetraor penta-azaindenes and in particular those which are substituted with hydroxyl or amino groups are also suitable for use as stabilizers. Compounds of this type are described in the article by Birr, Z. Wiss. Phot. 47, 2-58 (1952). Other suitable stabilizers include heterocyclic mercapto compounds, e.g. phenylmercapto tetrazole, quaternary benzothiazole derivatives, benzotriazole and the like.

The emulsions may be hardened in the usual manner, for example with formaldehyde or halosubstituted aldehydes which contain a carboxyl group, such as mucobromic acid, diketones, methane sulfonic acid esters, dialdehydes and the like.

EXAMPLE 1 A silver chlorobrornide gelatin emulsion (20 mol percent of AgBr) which is unwashed and which contains per liter 0.18 mol of silver halide, 2 ml. of a 1% alcoholic solution of 1-phenyl-5-mercapto-tetrazole, 20 ml. of a 10% aqueous saponin solution and 2 ml. of a 30% aqueous Formalin solution is divided into 5 portions. To each portion is added an anti-bronzing agent of the present invention in form of a solution in dimethylformamide. De-

tails are given in the following table.

The emulsions are applied onto a baryta-coated paper support. The final dried layer contains 1.4 g. silver per square meter in the form of silver halide.

Comparison strips of the photographic material thus obtained is exposed in a sensitometer customarily employed in the art. The exposed samples are developed in a developer of the following composition (temperature 18 0., developing time seconds) 1 g. of p-methylaminophenol 3 g. of hydroquinone 13 g. of anhydrous sodium sulfite 26 g. of sodium anhydrous carbonate 1 g. of potassium bromide dissolved in water and made up to 1000 ml.

The developed material is fixed for 10 minutes in an aqueous solution of sodium thiosulfate and rinsed.

The moist material is dried on a high gloss press heated to 130 C. Whereas the high gloss drying causes a color change from brown to greenish brown to blue in the control sample (without addition), the brown image tones do not change if a compound according to the invention is present. The maximum density of the different materials is determined with a densitometer of an air-dried sample as compared with a material dried on a glazing press.

The following results are obtained:

Maximum density Concentra- Dried on tion, high-gloss mgJl. Air dried density Control sample 0 1. 98 1. 71 Compound number:

EXAMPLE 2 Maximum density Concentra- Dried on tion, high-gloss mg./l Air dried density Control sample 0 1. 74 1. 53 Compound number:

EXAMPLE 3 Comparison strips of the photographic material prepared as described in Example 1 however, having a silver coating of 1.6 g./m. which do not contain any antibronzing agents are developed in different developer compositions.

The developer had the basic composition as described in Example 1. The diiferent samples, however, contain an anti-bronzing agent of the present invention in the amount indicated in the following table. The process is accomplished as described in Example 1. The following results are obtained:

Maximum density Coneentra- Dried on tion, high-gloss mg./l. Air dried density Control sample 0 2. 28 1. 71 Compound number:

Whereas the high gloss drying produces a color change to a color varying from greenish brown to blue in the control sample, the warm brown image tone remains unchanged when developed in a developer containing an anti-bronzing agent.

EXAMPLE 4 The experiments are performed as described in Example 3 with the exception however, that the control sample of Example 2 is used as photographic material and that the anti-bronzing agents are added to a fixing bath of the following composition:

Fixing bath 200 g. of sodium thiosulfate cryst. 20 g. of potassium rnetabisulfite dissolved in water and made up to 1000 ml.

The fixing bath is divided into 3 equal portions before fixing. The compounds indicated in the table below are added to these parts, and the material is fixed therein for minutes and then rinsed in the usual way. The following results are obtained:

1. In a process for the production of photographic silver images by exposing a photographic material which contains at least one supported silver halide emulsion layer, developing, fixing and drying, the improvement consisting of hot drying the processed layer containing the silver image in efiective contact with a dimercaptopyraZolo-pyrimidine of the following formula:

or the tautomeric thion compounds wherein R=an alkyl group containing 1-12 carbon atoms, a radical of the phenyl or naphth'yl series, cycloalkyl, triazinyl or pyrimidyl. 2. The process of claim 1, wherein the silver halide emulsion layer contains the dimercapto-pyrazolo-pyrimidine.

3. The process of claim 1, wherein a processing bath contains the dimercapto-pyrazolo-pyrimidine.

4. Light-sensitive photographic material having at least one supported silver halide emulsion layer which contains a dimercapto-pyrazolopyrimidine of the following formula:

i FN NW I N or the tautomeric thion compounds wherein 'R=an alkyl group containing 1-12 carbon atoms a radical of the phenyl or naphthyl series, cycloalkyl, trianinyl or pyrimidyl. 5. An aqueous photographic developing or fixing bath containing a dimercapto-pyrazolo-pyrimidine of the following formula:

or the tautomeric thion compounds wherein R=an alkyl group containing 1-12 carbon atoms, a radical of the phenyl or naphthyl series, cycloalkyl, triaizinyl or pyrimidyl.

References Cited UNITED STATES PATENTS 2 ,573,027 10/1951 Kendall 96-52 3,161,515 12/1964 Welsh 96--66.5

3,185,570 5/1965 Welsh 96-409 FOREIGN PATENTS 126,361 1/ 1948 Australia 96-52 701,054 12/1953 Great Britain 96-109 1,183,237 3/1970 Great Britain 96-409 NORMAN G. TORCHIN, Primary Examiner I. R. HIGHTOWER, Assistant Examiner US. Cl. X.R. 96--58, 66.5, 109 

